Calculators aside, you also need to consider the mouse and elephant analogy. Mice being very small have extremely rapid heart rates and elephants have very slow rates. So size matters.
Small and naturally skinny people tend to have faster than typical HRs and big, husky people have slower HRs. The calculator might be off by a few beats per minute, I doubt it's off as much as 10, but it's in the right ballpark.
I don't wear a HRM and I've never tested my max, so I have no idea what to shoot for. I long ago learned to run according to the rate of breathing and the feel of lactate buildup in the legs. What matters more to me is the resting HR. I try to take my pulse every morning when I wake up. This OFTEN takes several attempts. One, two, three, fo... Zzzz. If it's up a few beats then I'm not fully recovered from previous workouts and I need to back off on that day. If it's at the correct number then I'm good to go.